Like the Sony E 16/2.8, Sigma's 19mm lens is not particularly well suited for macro photography. The lens gives you magnification rate of ~0.14x at the MFD, which is not particularly exciting in the macro world. The lens does retain its sharpness in the center throughout the focusing range, so nothing should prevent you from shooting at or close to the MFD, but ultimately if you're even remotely interested in macro photography, this is not the lens for you.

f/2.8 @ MFD

f/8 @ MFC

Coma

As can be observed from the image crops below (taken ~1m focusing distance, f/2.8 and f/8 @ 3s exposire), Sigma shows minor degree of coma at f/2.8, which is reduced with stopped down apertures to pretty much non-existent levels